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/*
*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*
*/
package org.apache.qpid.server.queue;
import org.apache.log4j.Logger;
import java.util.List;
import java.util.ListIterator;
import java.util.concurrent.CopyOnWriteArrayList;
/**
* Holds a set of subscriptions for a queue and manages the round
* robin-ing of deliver etc.
*/
class SubscriptionSet implements WeightedSubscriptionManager
{
private static final Logger _log = Logger.getLogger(SubscriptionSet.class);
/**
* List of registered subscribers
*/
private List<Subscription> _subscriptions = new CopyOnWriteArrayList<Subscription>();
/**
* Used to control the round robin delivery of content
*/
private int _currentSubscriber;
/**
* Accessor for unit tests.
*/
int getCurrentSubscriber()
{
return _currentSubscriber;
}
public void addSubscriber(Subscription subscription)
{
_subscriptions.add(subscription);
}
/**
* Remove the subscription, returning it if it was found
* @param subscription
* @return null if no match was found
*/
public Subscription removeSubscriber(Subscription subscription)
{
boolean isRemoved = _subscriptions.remove(subscription); // TODO: possibly need O(1) operation here.
if (isRemoved)
{
return subscription;
}
else
{
debugDumpSubscription(subscription);
return null;
}
}
private void debugDumpSubscription(Subscription subscription)
{
if (_log.isDebugEnabled())
{
_log.debug("Subscription " + subscription + " not found. Dumping subscriptions:");
for (Subscription s : _subscriptions)
{
_log.debug("Subscription: " + s);
}
_log.debug("Subscription dump complete");
}
}
/**
* Return the next unsuspended subscription or null if not found.
*
* Performance note:
* This method can scan all items twice when looking for a subscription that is not
* suspended. The worst case occcurs when all subscriptions are suspended. However, it is does this
* without synchronisation and subscriptions may be added and removed concurrently. Also note that because of
* race conditions and when subscriptions are removed between calls to nextSubscriber, the
* IndexOutOfBoundsException also causes the scan to start at the beginning.
*/
public Subscription nextSubscriber(AMQMessage msg)
{
if (_subscriptions.isEmpty())
{
return null;
}
try {
final Subscription result = nextSubscriber();
if (result == null) {
_currentSubscriber = 0;
return nextSubscriber();
} else {
return result;
}
} catch (IndexOutOfBoundsException e) {
_currentSubscriber = 0;
return nextSubscriber();
}
}
private Subscription nextSubscriber()
{
final ListIterator<Subscription> iterator = _subscriptions.listIterator(_currentSubscriber);
while (iterator.hasNext()) {
Subscription subscription = iterator.next();
++_currentSubscriber;
subscriberScanned();
if (!subscription.isSuspended()) {
return subscription;
}
}
return null;
}
/**
* Overridden in test classes.
*/
protected void subscriberScanned()
{
}
public boolean isEmpty()
{
return _subscriptions.isEmpty();
}
public boolean hasActiveSubscribers()
{
for (Subscription s : _subscriptions)
{
if (!s.isSuspended()) return true;
}
return false;
}
public int getWeight()
{
int count = 0;
for (Subscription s : _subscriptions)
{
if (!s.isSuspended()) count++;
}
return count;
}
/**
* Notification that a queue has been deleted. This is called so that the subscription can inform the
* channel, which in turn can update its list of unacknowledged messages.
* @param queue
*/
public void queueDeleted(AMQQueue queue)
{
for (Subscription s : _subscriptions)
{
s.queueDeleted(queue);
}
}
int size() {
return _subscriptions.size();
}
}
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